UC San Diego UC San Diego Previously Published Works Title Drones in archaeology: Integrated data capture, processing, and dissemination in the al- ula valley, Saudi Arabia Permalink https://escholarship.org/uc/item/8d67642f Journal Near Eastern Archaeology, 77(3) ISSN 1094-2076 Authors Smith, NG Passone, L Al-Said, S et al. Publication Date 2014 DOI 10.5615/neareastarch.77.3.0176 Peer reviewed eScholarship.org Powered by the California Digital Library University of California Drones in Archaeology: Integrated Data Capture, Processing, and Dissemination in the al-Ula Valley, Saudi Arabia Neil G. Smith, Luca Passone, Said al-Said, Mohamed al-Farhan, and Tomas E. Levy n late 2013, a joint archaeological and computer vision initial results and methodology including the use of UAVs and project was initiated to digitally capture the archaeological modern advances in remote sensing computational techniques. remains in the al-Ula valley, Saudi Arabia. The goal of our Iteam of archeologists and computer scientists is to integrate Dedan – A City on the Crossroads of Ancient 3D scanning technologies to produce 3D reconstructions of Arabia and Modern Technology archaeological sites. Unmanned Aerial Vehicles (UAVs) serve Once an integral part of the North-South trade artery of the Ara- as the vehicle which makes this scanning possible. UAVs allow bian Peninsula, ancient Dedan was one of the most impressive the acquisition of 3D data as easily from the air as from the and extensive eighth century b.c.e.–frst century c.e. trade cen- ground. This project focuses on the recent excavations carried ters in Saudi Arabia (fg. 1). Nestled between the rugged red sand- out in ancient Dedan by King Saud University and the coun- stone mountains and lush date palm farms, the ruins of Dedan try’s conservation of the Lihyanite “lion tombs” carved into and their excavation make an ideal open air museum for tourists the ancient city’s cliff faces. Over the next several years this that have the rare privilege to visit the archaeological site. Te site will be used as a test bed to validate the potential of this ruins of Dedan (known locally as Al-Khuraybah) is located 4 km emerging technology for rapid cultural heritage documentation. north of the modern city al-Ula (26.6549º, 37.9131º, WGS1984). We additionally scanned several areas in Mada’in Saleh, an Dedan is strategically located in the al-Ula oasis adjacent to Wadi ancient Nabatean city filled with monumental carved sand- al-Qara where abundant water resources could be harvested for stone tomb facades, rivaled only by the capital of the Nabatean agriculture. Te ruins stretch for ca. 2 km around the eastern face empire: Petra. of a sandstone mountain range called Jabal Dedan. Te central Under the King Saud University’s Dedan (al-Ula) Archaeo- rectangular palace at its northern end as well as the“lion tombs” logical Excavation Project (al-Said 2009) and the Saudi Com- (of the Lihyanite kingdom, ffh century b.c.e.) carved into the mission for Tourism and Antiquities (SCTA), an initial digital clif face at the southern end are visible from satellite imagery. scan using low altitude fying UAVs was conducted at Dedan Te settlement of al-Khuraybah (Dedan) is the ancient capital (Khurayba) and Mada’in Saleh. In this article, we present our of the Dedanite kingdom (eighth–sixth centuries b.c.e.) and later 176 NEAR EASTERN ARCHAEOLOGY 77:3 (2014) the primary trading center of the Lihyanite kingdom (sixth–frst Te application of UAVs to archaeology is an emerging tech- centuries b.c.e.) until its collapse and abandonment in the frst nology. Lambers et al. (2007) and Guidi et al. (2008) were some century b.c.e. partially accelerated by a documented earthquake of the frst to use airborne photogrammetry in archaeological re- in the region (al-Said 2010). It was at this time that the Nabate- search to generate highly detailed 3D reconstructions, orthopho- ans took control of the area and focused the lucrative incense tos, and digital elevation models. Tis was followed by a number trade through Hegra (Mada’in Saleh) located 30 km north of De- of projects that directly sought to employ UAVs for aerial photo- dan. Over the past eight seasons of excavation an extensive area grammetric capture (Barazzetti et al. 2010; Irschara et al. 2010; of Dedan's ruins were exposed. Excavation and conservation has EisenBeiss and Sauerbier 2010; Levy et al. 2010; Remondino et been conducted by King Saud University with principal inves- al. 2011). Our own work, (Levy et al. 2010; Levy et al. 2012) has tigators Dr. Said al-Said and Dr. Abdulaziz Saud al-Ghazzi. Al- undergone a rapid evolution as new technology emerged and we though conservation techniques have been employed to protect adopted it into our feld recording methods. In 2000, we started the site, the majority of the walls constructed used mud-brick with boom systems and the frst commercially available digital and with the harsh weather conditions in al-Ula, it is inevitable cameras, followed in 2006 with our frst aerial balloon, and most that the structures will eventually decay and change in appear- recently with UAVs. ance. Considering these factors, the digital documentation of Aerial scanning’s contribution to the archaeological feld is its Dedan poses a solution both ability to achieve perspectives for documentation and vir- of architecture not possible tual site observation by both from ground scanning. Many archaeologists and tourists. cultural heritage sites and es- pecially archaeological exca- Unmanned Aerial vations contain a high level of Vehicles (UAVs) occlusion. Occlusion is detri- and Archaeology mental to scanning because A key component of our proj- anything that is concealed by ect is the development of a another object is not scanned. streamlined scanning system It results in large gaps or holes using UAVs for archaeology. in the data that can only be A UAV is an aerial vehicle resolved by conducting more (plane, helicopter, blimp) that scans from diferent loca- does not have a human pilot tions. Archaeological sites on board but is controlled re- are very complicated to scan motely. Some UAVs are capa- because they ofen consist of ble of autonomously follow- walls and structures that oc- ing a pre-programmed fight clude the majority of the site. path maintaining altitude and Even with multiple scans it is speed delivering images with not always possible to scan the correct overlap for 3D re- particular areas and achieve construction. Until recently, Figure 1. Map of northern Saudi Arabia, with research areas and sites highlighted. comprehensive capture. UAVs consisted primarily of However, whether it is ledges diferent types of planes or he- blocking the upper portions licopters that required extensive operational experience. For our of a carving or a complex system of small rooms within an ex- low altitude scanning we used a new type of UAV called a multi- cavated site, these areas are easily viewed from the air (see fgs. rotor copter. A multirotor copter uses between three to eight mo- 2–3). A large area can be captured in minimal time using aerial tor controlled counter-rotating propellers to balance itself and to scanning with limited occlusion. Additionally, aerial scanning be able to move in all degrees of freedom. A multirotor with four allows the capture of sites from the same perspective needed for propellers is called a quad-copter and by extension an octo-cop- publication: as top-down architectural drawings. Tey provide ter would employ eight propellers and motors. A multirotor re- a comprehensive layout of a site revealing how architecture and quires less fight training and with added GPS and a barometric terrain are interconnected. (altitude) sensor they hold their position even in strong winds. Similar to helicopters, a quad-copter can take of and land within The Technology Behind the UAV a small area with the ability to rotate and move in all directions. Over the past year, our team has been developing the hardware Te amount and size of propellers provides a tradeof between and sofware required to conduct automated aerial 3D scanning. payloads (e.g. size of camera that can be mounted) and difer- Te UAV provides the means to capture images from the air but ent fight times to be achieved. Tese features make a multirotor it is the sofware used to convert these 2D images into 3D mod- UAV a highly confgurable platform for aerial capture of com- els and merge them with ground scans that makes the technol- plex archaeological sites requiring multiple angles. ogy revolutionary. NEAR EASTERN ARCHAEOLOGY 77:3 (2014) 177 Figure 2 Figure 3 computer vision algorithms that automatically detect matching features in images (SIFT: Lowe 2004; Wu 2007) and efciently compute camera intrinsic parameters using a least squares ap- proximation called Bundle Adjustment (Brown and Lowe 2005; Hartley and Zisserman 2003; Snavely 2006; Wu 2011). SfM re- constructs a sparse point cloud and calculates camera positions We use a technique from the feld of computer vision called that allow the computation of dense point clouds and trian- Structure from Motion (SfM) to do the frst stage of 3D recon- gulated meshes using Multi-View Stereopsis (Furukawa and struction. Structure from Motion refers to the method of extract- Ponce 2007; Hartley and Zisserman 2003). Rather than stand- ing a 3D structure from many overlapping digital images. Begin- ing in a fxed position and capturing 3D data, SfM algorithms ning in the twenty-frst century, SfM emerged as a new photo- use a change in camera position for each image to fnd the dis- grammetric technique for 3D reconstruction that uses robust tance (motion) between them and at the same time triangulate 178 NEAR EASTERN ARCHAEOLOGY 77:3 (2014) the 3D positions of pixels matched in overlapping images.